The present invention relates in general to laser processing of workpieces such as semiconductor devices and more particularly concerns processing of DRAMS, memories, and programmable devices by cutting fuses or links.
Laser systems have been used for many years in the fabrication of DRAMS and programmable devices. In DRAM production, for example, redundant memory is programmed by using a focused laser beam to cut fuses or links in the memory in order to replace defective memory cells. The programming is accomplished by disconnecting the fuses or links using a laser pulse generated by a diode pumped Q-switched YAG (or YLF) laser.
Recent semiconductor devices have link geometries typically about 1 .mu.m wide by 5 .mu.m long. These links may be located in groups of horizontally aligned links and vertically aligned links. A laser having 3-5 .mu.m laser spot size may be used to disconnect such a link using a single laser pulse. By appropriately selecting the laser energy, the spot size, the laser pulse width, and the wavelength of the laser beam, it is possible to optimize laser parameters in order to achieve the cleanest and most reliable link disconnect.
The quality of a link disconnect may be evaluated by visually inspecting the blasted link. One measure of practicality in fuse or link disconnect is the energy cutting range or "energy window," which is the range of energies per pulse over which clean and reliable link cutting can be achieved. The laser energy that is used to process a semiconductor device can be set at the center of the predicted energy window, which may differ somewhat from the actual energy window due to process variations such as the thickness of the link material, the thickness of oxide material located on top of the link, laser instability, errors in the positioning of the laser beam, and focusing errors.
Many diode-pumped solid-state lasers used in laser processing systems are linearly polarized. Certain laser processing systems use circularly polarized laser beams rather than linear polarized laser beams.